There are many different types of optical recording elements known. In most dye-based recording layers, the mode of operation requires that the recording layer have a high absorption at the wave length of the recording laser, to maximize the energy absorbed, and the resulting marks from the write process have high reflectivity. This is achieved by having a reflective layer in back of the dye layer and ablating or fading the dye in the process of recording making highly reflective marks.
A current popular form of optical storage of information is the compact disc or CD. On these disks the digital information is stored in the form of low reflectivity marks, at the read wavelength, on an otherwise highly reflective background. This is the exact opposite of the above described optical recording materials. In this format, the optical information is most often in the form of read only memory or ROM. Optical information is not recorded in real time but rather is produced by press molding. In a typical process, the optical recording substrate is first press molded with a master containing the digital information to be reproduced. The thus formed information is then overcoated with a reflective layer and then with an optional protective layer. In those areas having the deformations or pits, the reflectivity is lower than in those areas not having the deformations.
It is desirable to produce writable optical recording media which, when recorded in real time, produces a record that mimics the conventional CD on read out. In this manner, information can be added to the CD and the CD can be used on conventional CD players.
One recently disclosed system of this type is the so called "Photo CD". In this system, conventional photographic film is first processed in a conventional manner. Then, the images from the film are digitized and the digital information is recorded in a CD readable form on an optical recording material. Images can then be played back on a CD type player into a conventional television. Since a CD has a capacity for a number of digitized images that is greater than the typical roll of consumer film, it is anticipated that the user will want to add images in multiple sessions to a CD. Thus the need for recordable, CD compatible optical recording material.
One method for forming a recordable element that mimics conventional mold pressed CD elements is to provide a heat deformable support having thereon, in order, a layer of a dye that absorbs recording radiation and a reflective layer. Exposure of the recording layer through the support by the recording beam heats the recording layer to an extent that it is said that the surface of the heat deformable support just adjacent to the recording layer surface is deformed. Materials of this type are described in U.S. Pat. No. 4,940,618, European Patent Application 0,353,393 and Canadian Patent Application 2,005,520.
Commercially useful materials for elements have stringent requirements. One of these requirements is layer integrity. Since the Photo CD is a consumer product, it must be capable of withstanding extreme environments. Between the time the original images are recorded on the Photo CD and the time subsequent images are added, the CD might be handled quite extensively. The recording layer must have sufficient cohesive strength within the layer and sufficient adhesive strength between the adjacent layers to retain its integrity through the handling process. In general, all monomeric dyes have very limited cohesive and/or adhesive strengths toward the adjacent layers, especially toward the reflective layer.
In the U.S. and the European applications mentioned above, the preferred dyes for the recording layer are indoledicarbocyanine dyes. However, this type of dye has less than the desired stability and the dye layer can be separated from the reflective gold layer with very little force. Thus, there is a continuing need for optical recording materials that have the necessary optical characteristics so that they are CD compatible and yet have good adhesive and cohesive characteristics It is to the solution to this problem that the present invention is directed.
Two patents that disclose the use of polymeric dyes for optical recording are: U.S. Pat. No. 4,680,375 and U.S. Pat. No. 4,666,819. The polymeric dyes disclosed in these patents do not include metallized dyes, nor do they include copolymers of metallized dyes and cyanine dyes. The polymeric dyes of these patents do not possess the correct optical constants for compliance with CD-writable media, nor are they stabilized to light. Nor does the prior art disclose or discuss in any way the primary advantage of this invention, which is to improve the physical properties of the write layer by improving the cohesive and/or adhesive properties of the layer.